GROWING ZONES

The warming trends of the past decades don’t just mean unusual weather events. There’s another consequence that is more subtle but has significant implications for equine health: a change in the growing seasons.

The latest version of the U.S. Department of Agriculture plant hardiness zone map, released in 2012, shows that all the plant zones have shifted north.

Based on average annual minimum winter temperatures, the map helps gardeners and other growers determine which plants will grow well in their region. The 2012 edition was based on an analysis of winter temperatures for the period 1976 to 2005, updating a 1990 version of the map, which covered 1974 to 1986.

This change in zones means that some northern areas now have longer growing seasons, which in turn extends the risk period for pastureinduced laminitis.

Many grasses grow as long as the temperature stays above about 50 degrees Fahrenheit. If your horse is prone to pasture laminitis, it’s no longer enough to judge your horse’s risk based solely on the calendar. Instead, pay close attention to the weather patterns and growth of your fields. Growth that used to be expected in late April, for instance, may occur in mid-March under warmer conditions. Similarly, grasses may grow later into the fall.

This warming trend doesn’t appear to be reversing itself anytime soon, so these adjusted risk periods for laminitis are probably here to stay.